Endothelin

Interleukin-33, endothelin-1, and inflammatory parameters in chronic spontaneous urticaria

Background: Endothelin-1 (ET-1) and interleukin-33 (IL-33) can modulate the activation of mast cells and basophils in the pathophysiology of allergic diseases, interplaying with other mediators of "low-grade inflammation." Objective: To compare ET-1, IL-33, the neutrophil-lymphocyte ratio (NLR), eosinophil-lymphocyte ratio (ELR), platelet-lymphocyte ratio (PLR), eosinophil-basophil ratio (EBR), systemic immune inflammation index (SII), and system inflammation response index (SIRI) in patients with chronic spontaneous urticaria (CSU) and are antihistamine sensitive (AHS), antihistamine resistant (AHR), omalizumab sensitive (OmS), and omalizumab resistant (OmR). Methods: A prospective observational study enrolled 68 consecutive patients with CSU diagnosed and managed according to the dermatology section of the European Academy of Allergology and Clinical Immunology (EAACI), the European Union funded network of excellence, the Global Allergy and Asthma European Network (GA2LEN), the European Dermatology Forum (EDF), and the World Allergy Organization guidelines. Patients with a urticaria control test score of >12 are considered treatment sensitive, and ≤ 12 are considered resistant. The control group consisted of 20 sex-matched subjects without urticarial diseases. Total immunoglobulin E (IgE), antinuclear antibodies (ANA), thyroid stimulating hormone, antithyroid peroxidase, mean platelet volume (MPV), NLR, ELR, PLR, EBR, SII, SIRI, ET-1, and IL-33 were measured at the study entry and compared between the study groups. Results: Thirty AHS group, 38 AHR group, and 20 control group patients were included. The AHS, AHR, and control groups did not differ in demographic parameters, but the CSU groups were characterized by higher indicators of inflammation. In comparison with the AHS group, the AHR group was characterized by higher levels of IL-33 (p = 0.007), ET-1 (p = 0.032), C-reactive protein (p = 0.016), MPV (p = 0.002), and higher rates of positive ANA (p = 0.019). Of the 38 patients from the AHR group, 30 (79%) were included in the OmS group and 8 (21%) were included in the OmR group. The OmR group was characterized by higher levels of C-reactive protein (p = 0.022), EBR (p < 0.001), higher rates of ANA (p = 0.004), and lower levels of ET-1 (p = 0.025) than the OmS group. Conclusion: Our study did not confirm NRL, PRL, SII, and SIRI, PLR as the biomarkers of treatment response to antihistamines and/or omalizumab in CSU. Higher blood levels of IL-33 and ET-1 characterize AHR CSU.

Association between endothelin-1 and systemic lupus erythematosus: insights from a case-control study

Systemic lupus erythematosus (SLE) is a chronic rheumatic disorder. Endothelin-1, a vasoconstrictor, belongs to the endothelin family and is associated with vascular-related damages. To date, association between ET-1 and pathogenesis of SLE remains unclear. This case-control study was carried out by 314 SLE, 252 non-SLE diseases patients and 500 healthy controls. Serum ET-1, CCN3, IL-28B levels were detected by ELISA, and ET-1 gene polymorphisms (rs5369, rs5370, rs1476046, rs2070699, rs2071942, rs2071943, rs3087459, rs4145451, rs6458155, rs9369217) were genotyped with Kompetitive Allele-Specific PCR. SLE patients had high levels of ET-1, which were correlated with some clinical, laboratory features. Serum CCN3, IL-28B levels were higher in SLE patients, and ET-1 levels were positively correlated with the two cytokines. Rs5370, rs1476046, rs2070699, rs2071942, rs2071943, rs3087459, rs6458155 and rs2070699 were associated with SLE risk. Rs2070699 (T, TT) was related to SLE patients with alopecia. Rs5370 (T, TT, TG), rs1476046 (G,GA), rs2071942 (G,GA) and rs2071943 (G,GA) were associated with SLE patients with pericarditis, pyuria and fever manifestation, respectively. Rs3087459 (CC) and rs9369217 (TC) were related to SLE patients with positive anti-SSB antibody. Rs5369 (AA) was associated with IgG and CRP levels in SLE patients. In conclusion, elevated serum ET-1 in SLE patients may be a potential disease marker, and its gene polymorphisms were related to SLE susceptibility.

Endothelin Receptor Antagonists in Kidney Disease

Endothelin (ET) is found to be increased in kidney disease secondary to hyperglycaemia, hypertension, acidosis, and the presence of insulin or proinflammatory cytokines. In this context, ET, via the endothelin receptor type A (ET_A) activation, causes sustained vasoconstriction of the afferent arterioles that produces deleterious effects such as hyperfiltration, podocyte damage, proteinuria and, eventually, GFR decline. Therefore, endothelin receptor antagonists (ERAs) have been proposed as a therapeutic strategy to reduce proteinuria and slow the progression of kidney disease. Preclinical and clinical evidence has revealed that the administration of ERAs reduces kidney fibrosis, inflammation and proteinuria. Currently, the efficacy of many ERAs to treat kidney disease is being tested in randomized controlled trials; however, some of these, such as avosentan and atrasentan, were not commercialized due to the adverse events related to their use. Therefore, to take advantage of the protective properties of the ERAs, the use of ET_A receptor-specific antagonists and/or combining them with sodium-glucose cotransporter 2 inhibitors (SGLT2i) has been proposed to prevent oedemas, the main ERAs-related deleterious effect. The use of a dual angiotensin-II type 1/endothelin receptor blocker (sparsentan) is also being evaluated to treat kidney disease. Here, we reviewed the main ERAs developed and the preclinical and clinical evidence of their kidney-protective effects. Additionally, we provided an overview of new strategies that have been proposed to integrate ERAs in kidney disease treatment.

Controls of Central and Peripheral Blood Pressure and Hemorrhagic/Hypovolemic Shock

The pressure exerted on the heart and blood vessels because of blood flow is considered an essential parameter for cardiovascular function. It determines sufficient blood perfusion, and transportation of nutrition, oxygen, and other essential factors to every organ. Pressure in the primary arteries near the heart and the brain is known as central blood pressure (CBP), while that in the peripheral arteries is known as peripheral blood pressure (PBP). Usually, CBP and PBP are correlated; however, various types of shocks and cardiovascular disorders interfere with their regulation and differently affect the blood flow in vital and accessory organs. Therefore, understanding blood pressure in normal and disease conditions is essential for managing shock-related cardiovascular implications and improving treatment outcomes. In this review, we have described the control systems (neural, hormonal, osmotic, and cellular) of blood pressure and their regulation in hemorrhagic/hypovolemic shock using centhaquine (Lyfaquin^®) as a resuscitative agent.

Sovateltide Mediated Endothelin B Receptors Agonism and Curbing Neurological Disorders

Neurological/neurovascular disorders constitute the leading cause of disability and the second leading cause of death globally. Major neurological/neurovascular disorders or diseases include cerebral stroke, Alzheimer’s disease, spinal cord injury, neonatal hypoxic-ischemic encephalopathy, and others. Their pathophysiology is considered highly complex and is the main obstacle in developing any drugs for these diseases. In this review, we have described the endothelin system, its involvement in neurovascular disorders, the importance of endothelin B receptors (ETBRs) as a novel potential drug target, and its agonism by IRL-1620 (INN—sovateltide), which we are developing as a drug candidate for treating the above-mentioned neurological disorders/diseases. In addition, we have highlighted the results of our preclinical and clinical studies related to these diseases. The phase I safety and tolerability study of sovateltide has shown it as a safe and tolerable compound at therapeutic dosages. Furthermore, preclinical and clinical phase II studies have demonstrated the efficacy of sovateltide in treating acute ischemic stroke. It is under development as a first-in-class drug. In addition, efficacy studies in Alzheimer’s disease (AD), acute spinal cord injury, and neonatal hypoxic-ischemic encephalopathy (HIE) are ongoing. Successful completion of these studies will validate that ETBRs signaling can be an important target in developing drugs to treat neurological/neurovascular diseases.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

The Class III PI3K/Beclin-1 Autophagic Pathway Participates in the mmLDL-Induced Upregulation of ETA Receptor in Mouse Mesenteric Arteries

Minimally modified low-density lipoprotein (mmLDL) is a risk factor for cardiovascular diseases. The current study explored the effect of mmLDL on the endothelin type A (ETA) receptor in mouse mesenteric arteries in vivo, as well as the role of autophagy in this process. mmLDL was injected via the caudal vein, and the Class III PI3K autophagic pathway inhibitor 3-methyladenine (3-MA) was injected intraperitoneally. The animals were divided into physiological saline (NS), mmLDL, and mmLDL + 3-MA groups. The dose-effect curve of endothelin-1- (ET-1-) induced mesenteric artery contraction was measured using myography, while ET_A receptor mRNA expression was detected using real-time polymerase chain reactions, and the protein levels of the ET_A receptor, class III PI3K, Beclin-1, LC3 II/I, p62, NF-κB, and p-NF-κB were observed using Western blot analysis. mmLDL significantly strengthened ET-1-induced contraction (the E_max value increased from 184.87 ± 7.46% in the NS group to 319.91 ± 20.31% in the mmLDL group (P < 0.001), and the pEC₅₀ value increased from 8.05 ± 0.05 to 9.11 ± 0.09 (P < 0.01). In addition to upregulating the protein levels of Class III PI3K, Beclin-1, and LC3 II/I and downregulating that of p62, mmLDL significantly increased the mRNA expression and protein level of the ET_A receptor and increased the protein level of p-NF-κB. However, these effects were significantly inhibited by 3-MA. mmLDL activates autophagy via the Class III PI3K/Beclin-1 pathway and upregulates the ET_A receptor via the downstream NF-κB pathway. Understanding the effect of mmLDL on the ET_A receptor and the underlying mechanisms may provide a new idea for the prevention and treatment of cardiovascular diseases.

Biomechanical Forces and Oxidative Stress: Implications for Pulmonary Vascular Disease

Significance: Oxidative stress in the cell is characterized by excessive generation of reactive oxygen species (ROS). Superoxide (O₂^-) and hydrogen peroxide (H₂O₂) are the main ROS involved in the regulation of cellular metabolism. As our fundamental understanding of the underlying causes of lung disease has increased it has become evident that oxidative stress plays a critical role. Recent Advances: A number of cells in the lung both produce, and respond to, ROS. These include vascular endothelial and smooth muscle cells, fibroblasts, and epithelial cells as well as the cells involved in the inflammatory response, including macrophages, neutrophils, eosinophils. The redox system is involved in multiple aspects of cell metabolism and cell homeostasis. Critical Issues: Dysregulation of the cellular redox system has consequential effects on cell signaling pathways that are intimately involved in disease progression. The lung is exposed to biomechanical forces (fluid shear stress, cyclic stretch, and pressure) due to the passage of blood through the pulmonary vessels and the distension of the lungs during the breathing cycle. Cells within the lung respond to these forces by activating signal transduction pathways that alter their redox state with both physiologic and pathologic consequences. Future Directions: Here, we will discuss the intimate relationship between biomechanical forces and redox signaling and its role in the development of pulmonary disease. An understanding of the molecular mechanisms induced by biomechanical forces in the pulmonary vasculature is necessary for the development of new therapeutic strategies.

ECE-1 overexpression in head and neck cancer is associated with poor tumor differentiation and patient outcome

BACKGROUND

Endothelin-converting enzyme-1 (ECE-1) primarily converts big endothelins (ETs) into active endothelin-1 (ET-1). However, the expression pattern and prognostication status of ECE-1 in head and neck cancer (HNC) are enigmatic. In this study, we investigated ECE-1 expression and assessed the roles of ECE-1 as a predictor for HNC differentiation and prognosis.

MATERIALS AND METHODS

ECE-1 expressions were evaluated by immunohistochemical analysis using a tissue microarray (TMA) composed of 100 cases of head and neck squamous cell carcinoma. The correlation of ECE-1 expression with clinicopathologic variables and patient outcomes was analyzed.

RESULTS

ECE-1 may be overexpressed in HNC carcinoma cells. Higher ECE-1 level was detected more frequently in moderately to poorly differentiated tumors and showed a lower differentiation category compared to the G1 cases (p = 0.015); this finding was further confirmed by an adjusted odds ratio (OR) of 4.071 (p = 0.042). Moreover, Kaplan-Meier survival analyses showed that a higher ECE-1 expression was associated with a poorer survival in patients with HNC (p < 0.0001). On multivariate Cox proportional hazards models analysis, ECE-1 of high expression proved to be an independent prognostic factor with a hazard ratio (HR) of 3.985 (p < 0.001).

CONCLUSION

Our data provide the first evidence that overexpression of ECE-1 in HNC is a predictor of poor tumor differentiation and prognosis.

New drugs and emerging therapeutic targets in the endothelin signaling pathway and prospects for personalized precision medicine

During the last thirty years since the discovery of endothelin-1, the therapeutic strategy that has evolved in the clinic, mainly in the treatment of pulmonary arterial hypertension, is to block the action of the peptide either at the ET(A) subtype or both receptors using orally active small molecule antagonists. Recently, there has been a rapid expansion in research targeting ET receptors using chemical entities other than small molecules, particularly monoclonal antibody antagonists and selective peptide agonists and antagonists. While usually sacrificing oral bio-availability, these compounds have other therapeutic advantages with the potential to considerably expand drug targets in the endothelin pathway and extend treatment to other pathophysiological conditions. Where the small molecule approach has been retained, a novel strategy to combine two vasoconstrictor targets, the angiotensin AT(1) receptor as well as the ET(A) receptor in the dual antagonist sparsentan has been developed. A second emerging strategy is to combine drugs that have two different targets, the ET(A) antagonist ambrisentan with the phosphodiesterase inhibitor tadalafil, to improve the treatment of pulmonary arterial hypertension. The solving of the crystal structure of the ET(B) receptor has the potential to identify allosteric binding sites for novel ligands. A further key advance is the experimental validation of a single nucleotide polymorphism that has genome wide significance in five vascular diseases and that significantly increases the amount of big endothelin-1 precursor in the plasma. This observation provides a rationale for testing this single nucleotide polymorphism to stratify patients for allocation to treatment with endothelin agents and highlights the potential to use personalized precision medicine in the endothelin field.

Relationship between serum vascular cell adhesion molecule-1 and endothelin-1 levels with organ involvement and disease activity in systemic lupus erythematosus patients

Background

Endothelial dysfunction plays an important role in pathogenesis of systemic lupus erythematosus (SLE). Considering the importance of serum soluble vascular cell adhesion molecule-1 as the most abundant of the circulating adhesion molecules increased as a result of endothelial dysfunction and the role of endothelin-1 in pathophysiology of SLE, this study aimed to evaluate serum soluble vascular cell adhesion molecule-1 and endothelin-1 levels in SLE patients compared to healthy subjects.

Methods

In this cross-sectional study, 60 SLE patients according to the Systemic Lupus International Collaborating Clinics classification criteria for SLE and 40 age and sex-matched healthy controls were included. In patients, clinical examination was performed and SLE disease activity index was assessed. Serum endothelin-1 and soluble vascular cell adhesion molecule-1 levels were measured using ELISA kits.

Results

The mean ± standard deviation age of patients and controls was 31.91 ± 7.66 and 33.20 ± 10.08 years, respectively. Compared to healthy controls, serum soluble vascular cell adhesion molecule-1 (1023.8 ± 352.96 vs. 866.06 ± 109.91) and endothelin-1 (77.83 ± 16.27 vs. 54.45 ± 12.01) was significantly higher in SLE patients ( P = 0.003 and P < 0.001, respectively). The most common organs involved in patients were skin, joint and kidney. There were no significant differences in serum soluble vascular cell adhesion molecule-1 and endothelin-1 levels according to organ involvement, activity of disease and the conventional serum markers of disease activity ( P > 0.05). There was no significant correlation between disease activity, organ involvement and negative or positivity of autoantibodies as well as serum complement with endothelin-1 and vascular cell adhesion molecule-1 levels ( P > 0.05).

Conclusions

Although our study revealed higher serum soluble vascular cell adhesion molecule-1 and endothelin-1 levels in SLE patients compared to healthy controls, there were no significant correlations between their serum levels with organ involvement and disease activity.

Endothelin-1, α-Klotho, 25(OH) Vit D levels and severity of disease in scleroderma patients

Considering the role of endothelin-1 (ET-1) in tissue remodeling and fibrosis during the development of scleroderma as well as the effect of α-Klotho in pathogenesis of calcinosis and/or endothelial cell injury and its correlation with severity of disease, this study aimed to evaluate serum ET-1, α-Klotho and 25(OH) vitamin D levels in patients with limited and diffuse scleroderma compared to healthy subjects. In this cross-sectional study, 60 scleroderma patients according to the ACR/EULAR 2013 criteria and 60 age- and sex-matched healthy controls were included. In patients, clinical examination was performed and Medsger severity scale was assessed. Serum ET-1, soluble α-Klotho and 25(OH)D₃ levels were measured using ELISA kits. The mean ± SD age of patients and controls was 46.2 ± 9.6 and 47.2 ± 7.0 years, respectively. Compared to healthy controls, serum ET-1 was significantly higher in SSc patients (p = 0.001); whilst serum α-Klotho and 25(OH)D₃ were significantly lower in patients (p = 0.001). The most common organs involved in patients were skin, lung, peripheral vascular and gastrointestinal system and the severity of involvement was mainly mild and/or moderate. There were no significant differences in serum ET-1 and α-Klotho levels according to the severity of different organ involvement (p > 0.05). There was no significant correlation between presence or absence of calcinosis and negative or positivity of auto-antibodies with ET-1, α-Klotho and 25(OH)D₃ levels. Although our study revealed higher serum ET-1 and lower serum α-Klotho levels in SSc patients compared to healthy controls, there were not any significant correlations between their serum levels with severity of organ involvement.

Aberrant methylated EDNRB can act as a potential diagnostic biomarker in sporadic colorectal cancer while KISS1 is controversial

Cancers are among the most serious threats of human health worldwide. Survival and mortality rates of colorectal cancer (CRC) strongly depend on the early diagnosis. The aberrant methylation pattern of genes as a diagnostic biomarker can serve as a practical option for timely detection and contribute subsequently to the enhancement of survival rate in CRC patients, since methylation changes are not only frequent but also can occur in initial tumorogenesis stages. It has been indicated that EDNRB and KISS1 genes are hypermethylated through progression and development of CRC. In current study, after extraction of genomic DNA from 45 paired tumor and adjacent non-cancerous tissue samples and treatment with bisulfite conversion, the methylation status of EDNRB and KISS1 CpG rich regions were assessed quantitatively using MS-HRM assay to determine practicability of these aberrant methylations for diagnosis of sporadic CRC and its discrimination from corresponding normal tissues. The results showed that the methylation distribution differences, comparing tumor tissues with their adjacent non-cancerous tissues, were statistically significant in all selected locations within EDNRB gene promoter (P < 0.001); they had also some correlations with tumor stage and grade. Nonetheless, methylation distribution in KISS1 gene CpG rich region revealed no statistically significant differences between CRC and adjacent non-cancerous tissues (P = 0.060). Overall, it can be concluded that aberrant methylated EDNRB can be a promising potential diagnostic biomarker for CRC, while KISS1 is controversial and needs to be more investigated.

Endothelial and Smooth Muscle Cell Interactions in the Pathobiology of Pulmonary Hypertension

In the pulmonary vasculature, the endothelial and smooth muscle cells are two key cell types that play a major role in the pathobiology of pulmonary vascular disease and pulmonary hypertension. The normal interactions between these two cell types are important for the homeostasis of the pulmonary circulation, and any aberrant interaction between them may lead to various disease states including pulmonary vascular remodeling and pulmonary hypertension. It is well recognized that the endothelial cell can regulate the function of the underlying smooth muscle cell by releasing various bioactive agents such as nitric oxide and endothelin-1. In addition to such paracrine regulation, other mechanisms exist by which there is cross-talk between these two cell types, including communication via the myoendothelial injunctions and information transfer via extracellular vesicles. Emerging evidence suggests that these nonparacrine mechanisms play an important role in the regulation of pulmonary vascular tone and the determination of cell phenotype and that they are critically involved in the pathobiology of pulmonary hypertension.

Endothelin receptor antagonists for persistent pulmonary hypertension in term and late preterm infants

BACKGROUND

Endothelin, a powerful vasoconstrictor, is one of the mediators in the causation of persistent pulmonary hypertension of the newborn (PPHN). Theoretically, endothelin receptor antagonists (ETRA) have the potential to improve the outcomes of infants with PPHN.

OBJECTIVES

To assess the efficacy and safety of ETRA in the treatment of PPHN in full-term, post-term and late preterm infants.To assess the efficacy and safety of selective ETRAs (which block only the ETA receptors) and non-selective ETRAs (which block both ETA and ETB receptors) separately.

SEARCH METHODS

CENTRAL (Cochrane Central Register of Controlled Trials), MEDLINE, EMBASE and CINAHL databases were searched until December 2015.

SELECTION CRITERIA

Randomised, cluster-randomised or quasi-randomised controlled trials were eligible.

DATA COLLECTION AND ANALYSIS

Two review authors independently searched the literature, selected the studies, assessed the risk of bias and extracted the data. A fixed-effect model was used for meta-analysis. We used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to assess the quality of evidence.

MAIN RESULTS

Two randomised controlled trials of ETRA met the inclusion criteria. Both studies utilized oral Bosentan. The first study was done in a setting where inhaled nitric oxide (iNO) therapy was not available. Forty-seven infants (≥ 34 weeks' gestation) were randomised to receive either Bosentan or placebo. The second study was a multicentre study where iNO therapy was the standard of care for PPHN. Twenty-one infants were randomised to receive either 'iNO plus Bosentan' or 'iNO plus placebo'.In the first study, there was no significant difference in the incidence of death before hospital discharge between the Bosentan and placebo groups (1/23 vs 3/14; RR 0.20, 95% CI 0.02 to 1.77; RD -0.17, 95% CI -0.40 to 0.06). A higher proportion of infants in the Bosentan group showed improvement in oxygenation index (OI) at the end of therapy (21/24 vs 3/15; RR 4.38, 95% CI 1.57 to 12.17; RD 0.68, 95% CI 0.43 to 0.92; number needed to treat for a beneficial outcome (NNTB) 1.5). The duration of mechanical ventilation was lower in the Bosentan group (4.3 ± 0.9 vs 11.5 ± 0.6 days; MD -7.20, 95% CI -7.64 to -6.76). There was no significant difference in adverse neurological outcomes at six months (0/23 vs 4/14; RR 0.07, 95% CI 0.00 to 1.20; RD -0.29, 95% CI -0.52 to -0.05). The study suffered from a high risk of attrition bias since 8/23 infants in the placebo group were excluded from various analyses. Since the protocol for the study could not be accessed, the study suffered from unclear risk of reporting bias.In the second study, there was no significant difference in the incidence of treatment failure needing extracorporeal membrane oxygenation (ECMO) between the 'iNO plus Bosentan' vs 'iNO plus placebo' groups (1/13 vs 0/8; RR 1.93, 95% CI 0.09 to 42.35; RD 0.08, 95% CI -0.14 to 0.30). There was no significant difference in the median time to wean from iNO ('iNO plus Bosentan': 3.7 days (95% CI 1.17 to 6.95); 'iNO plus placebo': 2.9 days (95% CI 1.26 to 4.23); P = 0.34). There were no significant differences in the OI 0, 3, 5, 12, 24, 48 and 72 hours of treatment between the groups. There were no significant differences in the time to complete weaning from mechanical ventilation (median 10.8 days (CI 3.21 to 12.21) versus 8.6 days (CI 3.71 to 9.66); P = 0.24). The study had unequal distribution to the Bosentan group (N = 13) and the placebo group (N = 8). The methods used for generating random sequence numbers and allocation concealment were unclear, resulting in unclear risk of selection bias.Both studies reported that Bosentan was well tolerated and no major adverse effects were noted. Data from the two studies was not pooled given the heterogenous nature of the clinical settings and the modalities used for the treatment of PPHN.Overall, the quality of evidence was considered low, given the small sample size of the included studies, the numerical imbalance between the groups due to randomisation and attrition, and unclear risk of bias on some of the important domains.

AUTHORS' CONCLUSIONS

There is inadequate evidence to support the use of ETRAs either as stand-alone therapy or as adjuvant to inhaled nitric oxide in PPHN. Adequately powered RCTs are needed.

Endothelin-1: Biosynthesis, Signaling and Vasoreactivity

Endothelin-1 (ET-1) is an extremely potent vasoconstrictor peptide originally isolated from endothelial cells. Its synthesis, mainly regulated at the gene transcription level, involves processing of a precursor by a furin-type proprotein convertase to an inactive intermediate, big ET-1. The latter peptide can then be cleaved directly by an endothelin-converting enzyme (ECE) into ET-1 or reach the active metabolite through a two-step process involving chymase hydrolyzing big ET-1 to ET-1 (1-31), itself needing conversion to ET-1 by neprilysin (NEP) to exert physiological activity. ET-1 signals through two G protein-coupled receptors, endothelin receptor A (ETA) and endothelin receptor B (ETB). Both receptors induce an increase in intracellular Ca(2+), mainly from the extracellular space through voltage-independent mechanisms, the receptor-operated channels and store-operated channels. ET-1 also induces signaling through epidermal growth factor receptor transactivation, oxidative stress induction, rho-kinase, and the activation (ETA) or inhibition (ETB) of the adenylate cyclase/cyclic adenosine monophosphate pathway. Arterial vasoconstriction is mediated mainly by the ETA receptor. ET-1, via endothelium-located ETB, relaxes arteries or constricts vessels following activation of the same receptor type on the smooth muscle, where it can interact with ETA. In addition, ETB-dependent vasoconstriction seems more prominent in the venous vasculature. A better understanding of how ET-1 is synthesized and how ETA and ETB receptors interact could help design better pharmacological agents in the treatment of cardiovascular diseases where targeting the ET-1 system is indicated.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.

Endothelin receptors and their antagonists

All three members of the endothelin (ET) family of peptides, ET-1, ET-2, and ET-3, are expressed in the human kidney, with ET-1 being the predominant isoform. ET-1 and ET-2 bind to two G-protein–coupled receptors, ET_A and ET_B, whereas at physiological concentrations ET-3 has little affinity for the ET_A receptor. The human kidney is unusual among the peripheral organs in expressing a high density of ET_B. The renal vascular endothelium only expresses the ET_B subtype and ET-1 acts in an autocrine or paracrine manner to release vasodilators. Endothelial ET_B in kidney, as well as liver and lungs, also has a critical role in scavenging ET-1 from the plasma. The third major function is ET-1 activation of ET_B in in the nephron to reduce salt and water re-absorption. In contrast, ET_A predominate on smooth muscle, causing vasoconstriction and mediating many of the pathophysiological actions of ET-1. The role of the two receptors has been delineated using highly selective ET_A (BQ123, TAK-044) and ET_B (BQ788) peptide antagonists. Nonpeptide antagonists, bosentan, macitentan, and ambrisentan, that are either mixed ET_A/ET_B antagonists or display ET_A selectivity, have been approved for clinical use but to date are limited to pulmonary hypertension. Ambrisentan is in clinical trials in patients with type 2 diabetic nephropathy. This review summarizes ET-receptor antagonism in the human kidney, and considers the relative merits of selective versus nonselective antagonism in renal disease.

Air pollution and children's health: sickle cell disease

The hallmarks of sickle cell disease are anemia and vasculopathy. The aim of this study was to assess the association between air pollution and children's emergency room visits of sickle cell patients. We adopted a case-crossover design. Daily counts of children's and adolescents' sickle cell disease emergency room visits from the pediatric emergency unit in São Paulo, Brazil, were evaluated from September 1999 to December 2004, matching by temperature, humidity and controlling for day of the week. Interquartile range increases of the four-day moving averages of PM10, NO2, SO2, CO, and O3 were associated with increases of 18.9% (95%CI: 11.2-26.5), 19% (95%CI: 8.3-29.6), 14.4% (95%CI: 6.5-22.4), 16,5% (95%CI: 8.9-24.0), and 9.8% (95%CI: 1.1-18.6) in total sickle cell emergency room visits, respectively. When the analyses were stratified by pain, PM10 was found to be 40.3% higher than in sickle cell patients without pain symptoms. Exposure to air pollution can affect the cardiovascular health of children and may promote a significant health burden in a sensitive group.

Involvement of endothelins in deoxycorticosterone acetate-salt hypertension through the modulation of noradrenergic transmission in the rat posterior hypothalamus

NEW FINDINGS

What is the central question of this study? Does ex vivo administration of endothelin-1 and endothelin-3 regulate noradrenergic transmission in the posterior hypothalamus of deoxycorticosterone acetate-salt hypertensive rats compared with normotensive rats? What is the main finding and its importance? Endothelin-1 and endothelin-3 enhanced diverse mechanisms leading to increased noradrenergic transmission in the posterior hypothalamus of deoxycorticosterone acetate-salt hypertensive rats. Unveiling the role of brain endothelins in hypertension would probably favour the development of new therapeutic targets for the treatment of essential hypertension, which still represents a challenging disease with high mortality. Brain catecholamines participate in diverse biological functions regulated by the hypothalamus. We have previously reported that endothelin-1 and endothelin-3 (ET-1 and ET-3) modulate catecholaminergic activity in the anterior and posterior hypothalamus of normotensive rats. The aim of the present study was to evaluate the interaction between endothelins and noradrenergic transmission in the posterior hypothalamus of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. We assessed the effects of ET-1 and ET-3 on tyrosine hydroxylase activity and expression, neuronal noradrenaline (NA) release, neuronal NA transporter (NAT) activity and expression, monoamine oxidase activity and NA endogenous content and utilization (as a marker of turnover) in the posterior hypothalamus of DOCA-salt hypertensive rats. In addition, levels of ETA and ETB receptors were assayed in normotensive and hypertensive rats. Results showed that tyrosine hydroxylase activity and total and phosphorylated levels, NAT activity and content, NA release, monoamine oxidase activity and NA utilization were increased in DOCA-salt rats. Both ET-1 and ET-3 further enhanced all noradrenergic parameters except for total tyrosine hydroxylase level and NA endogenous content and utilization. The expression of ETA receptors was increased in the posterior hypothalamus of DOCA-salt rats, but ETB receptors showed no changes. These results show that ET-1 and ET-3 upregulate noradrenergic activity in the posterior hypothalamus of DOCA-salt hypertensive rats. Our findings suggest that the interaction between noradrenergic transmission and the endothelinergic system in the posterior hypothalamus may be involved in the development and/or maintenance of hypertension in this animal model.

Endothelin@25 - new agonists, antagonists, inhibitors and emerging research frontiers: IUPHAR Review 12

Since the discovery of endothelin (ET)-1 in 1988, the main components of the signalling pathway have become established, comprising three structurally similar endogenous 21-amino acid peptides, ET-1, ET-2 and ET-3, that activate two GPCRs, ETA and ETB . Our aim in this review is to highlight the recent progress in ET research. The ET-like domain peptide, corresponding to prepro-ET-193-166 , has been proposed to be co-synthesized and released with ET-1, to modulate the actions of the peptide. ET-1 remains the most potent vasoconstrictor in the human cardiovascular system with a particularly long-lasting action. To date, the major therapeutic strategy to block the unwanted actions of ET in disease, principally in pulmonary arterial hypertension, has been to use antagonists that are selective for the ETA receptor (ambrisentan) or that block both receptor subtypes (bosentan). Macitentan represents the next generation of antagonists, being more potent than bosentan, with longer receptor occupancy and it is converted to an active metabolite; properties contributing to greater pharmacodynamic and pharmacokinetic efficacy. A second strategy is now being more widely tested in clinical trials and uses combined inhibitors of ET-converting enzyme and neutral endopeptidase such as SLV306 (daglutril). A third strategy based on activating the ETB receptor, has led to the renaissance of the modified peptide agonist IRL1620 as a clinical candidate in delivering anti-tumour drugs and as a pharmacological tool to investigate experimental pathophysiological conditions. Finally, we discuss biased signalling, epigenetic regulation and targeting with monoclonal antibodies as prospective new areas for ET research.

Homocysteine-induced attenuation of vascular endothelium-dependent hyperalgesia in the rat

We have recently demonstrated a role of the vascular endothelium in peripheral pain mechanism by disrupting endothelial cell function using intravascular administration of octoxynol-9, a non-selective membrane active agent. As an independent test of the role of endothelial cells in pain mechanisms, we evaluated the effect of homocysteine, an agent that damages endothelial cell function. Mechanical stimulus-induced enhancement of endothelin-1 hyperalgesia in the gastrocnemius muscle of the rat was first prevented then enhanced by intravenous administration of homocysteine, but was only inhibited by its precursor, methionine. Both homocysteine and methionine significantly attenuated mechanical hyperalgesia in two models of ergonomic muscle pain, induced by exposure to vibration, and by eccentric exercise, and cutaneous mechanical hyperalgesia in an ischemia-reperfusion injury model of Complex Regional Pain Syndrome type I, all previously shown responsive to octoxynol-9. This study provides independent support for a role of the endothelial cell in pain syndromes thought to have a vascular basis, and suggests that substances that are endothelial cell toxins can enhance vascular pain.

Itch mechanisms and circuits

The itch-scratch reflex serves as a protective mechanism in everyday life. However, chronic persistent itching can be devastating. Despite the clinical importance of the itch sensation, its mechanism remains elusive. In the past decade, substantial progress has been made to uncover the mystery of itching. Here, we review the molecules, cells, and circuits known to mediate the itch sensation, which, coupled with advances in understanding the pathophysiology of chronic itching conditions, will hopefully contribute to the development of new anti-itch therapies.

Hypermethylation of EDNRB promoter contributes to the risk of colorectal cancer

OBJECTIVE

Colorectal cancer (CRC) is one of the most common digestive malignancies in the world. EDNRB is a new candidate tumor suppressor gene which is often down-regulated or even silenced by promoter hypermethylation in various human cancers. However, the function of EDNRB gene in CRC remains unknown. In this study, we examined the expression and DNA methylation of EDNRB in CRC tissues.

METHODS

A total of 42 paired CRC and adjacent normal tissue samples were used to determine mRNA levels and DNA methylation status of EDNRB gene by qRT-PCR and methylation-specific PCR (MSP), respectively.

RESULTS

Our study showed that EDNRB promoter hypermethylation was more frequently in CRC tissues than in the normal tissues (92.86 versus 59.52, p = 0.001). Consequently, significantly lower level of EDNRB mRNA was found in CRC tumor samples than in normal samples (0.31 ± 0.91 versus 0.70 ± 1.18, p = 0.032).

CONCLUSIONS

Our results suggested that EDNRB promoter hypermethylation might downregulate its gene expression in CRC, and thus played an important role in the development of CRC.

THE VIRTUAL SLIDE

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/7420980471113303.

Themed section: endothelin

This themed section of the British Journal of Pharmacology contains reviews on recent developments in endothelin research arising from the Twelfth International Conference on Endothelin (ET-12). It includes the emerging role for endothelin-2 in the cardiovascular system, ovarian development, immunology and cancer. The action of endothelin on two key targets is discussed: the paracrine or autocrine regulation of contractility and growth in the heart and the role of endothelin in renal disease. Epidemiological studies have demonstrated cardiovascular disease and circulating levels of endothelin-1 are lower in premenopausal women than in men and evidence is presented for the contribution of sex differences in responses to the peptide. Transcription is the primary level of regulation of the endothelin gene; and current research on the epigenetic regulation of the endothelin pathway, including the silencing of the EDNRB gene encoding the ET(B) receptor during tumourigenesis, is reviewed.

LINKED ARTICLES

This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1. To view the previously published paper by Dhaun et al. visit http://dx.doi.org/10.1111/j.1476-5381.2012.02070.x.

Pivotal role of mouse mast cell protease 4 in the conversion and pressor properties of Big-endothelin-1

The serine protease chymase has been reported to generate intracardiac angiotensin-II (Ang-II) from Ang-I as well as an intermediate precursor of endothelin-1 (ET-1), ET-1 (1-31) from Big-ET-1. Although humans possess only one chymase, several murine isoforms are documented, each with its own specific catalytic activity. Among these, mouse mast cell protease 4 (mMCP-4) is the isoform most similar to the human chymase for its activity. The aim of this study was to characterize the capacity of mMCP-4 to convert Big-ET-1 into its bioactive metabolite, ET-1, in vitro and in vivo in the mouse model. Basal mean arterial pressure did not differ between wild-type (WT) and mMCP-4(-/-) mice. Systemic administration of Big-ET-1 triggered pressor responses and increased blood levels of immunoreactive (IR) ET-1 (1-31) and ET-1 that were reduced by more than 50% in mMCP-4 knockout (-/-) mice compared with WT controls. Residual responses to Big-ET-1 in mMCP-4(-/-) mice were insensitive to the enkephalinase/neutral endopeptidase inhibitor thiorphan and the specific chymase inhibitor TY-51469 {2-[4-(5-fluoro-3-methylbenzo[b]thiophen-2-yl)sulfonamido-3-methanesulfonylphenyl]thiazole-4-carboxylic acid}. Soluble fractions from the lungs, left cardiac ventricle, aorta, and kidneys of WT but not mMCP-4(-/-) mice generated ET-1 (1-31) from exogenous Big-ET-1 in a TY-51469-sensitive fashion as detected by high-performance liquid chromatography/ matrix-assisted laser desorption/ionization-mass spectrometry. Finally, pulmonary endogenous levels of IR-ET-1 were reduced by more than 40% in tissues derived from mMCP-4(-/-) mice compared with WT mice. Our results show that mMCP-4 plays a pivotal role in the dynamic conversion of systemic Big-ET-1 to ET-1 in the mouse model.

Endothelin-2, the forgotten isoform: emerging role in the cardiovascular system, ovarian development, immunology and cancer

Endothelin-2 [ET-2; also known as vasoactive intestinal contractor (VIC), in rodents] differs from endothelin-1 (ET-1) by only two amino acids, and unlike the third isoform, endothelin-3 (ET-3), it has the same affinity as ET-1 for both ET(A) and ET(B) receptors. It is often assumed that ET-2 would mimic the actions of the more abundant ET-1 and current pharmacological interventions used to inhibit the ET system would also block the actions of ET-2. These assumptions have focused research on ET-1 with ET-2 studied in much less detail. Recent research suggests that our understanding of the ET family requires re-evaluation. Although ET-2 is very similar in structure as well as pharmacology to ET-1, and may co-exist in the same tissue compartments, there is converging evidence for an important and distinct ET-2 pathway. Specifically is has been demonstrated that ET-2 has a key role in ovarian physiology, with ET-2-mediated contraction proposed as a final signal facilitating ovulation. Furthermore, ET-2 may also have a pathophysiological role in heart failure, immunology and cancer. Comparison of ET-2 versus ET-1 mRNA expression suggests this may be accomplished at the level of gene expression but differences may also exist in peptide synthesis by enzymes such as endothelin converting enzymes (ECEs) and chymase, which may allow the two pathways to be distinguished pharmacologically and become separate drug targets. LINKED ARTICLES This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Defining the affinity and receptor sub-type selectivity of four classes of endothelin antagonists in clinically relevant human cardiovascular tissues

AIMS

We have compared the endothelin receptor subtype affinity (K(D)) and selectivity of four structural classes of antagonists (peptide, sulphonamide-based, carboxylic acid-based, myceric acid-based) in human cardiovascular tissues to determine whether these are predicted by values reported for human cloned receptors. Additionally, affinities (K(B)) for these antagonists, determined in ET-1-mediated vasoconstriction assays in human blood vessels, were used to identify discrepancies between K(B) and K(D) determined in the same tissues.

MAIN METHODS

Competition binding experiments were carried out in sections of human left ventricle, coronary artery and homogenates of saphenous vein to determine K(D) values for structurally different ET(A)-selective (FR139317, BMS 182874, S97-139, sitaxentan, ambrisentan) and mixed (PD142893, Ro462005, bosentan, L-749329, SB209670) antagonists. Schild-derived values of antagonist affinity were obtained in vascular functional studies.

KEY FINDINGS

When compared with previously reported data in human cloned endothelin receptors, those antagonists reported to be ET(A)-selective exhibited even greater ET(A) selectivity in human ventricle (BMS 182874, sitaxentan, ambrisentan) that expressed both receptor subtypes. Those antagonists reported to have <100 fold selectivity in cloned receptors (PD142893, Ro-462005, bosentan, SB209670, L-749329) did not distinguish between receptor subtypes in human left ventricle. For antagonists where we determined affinity in vascular functional and binding assays (Ro462005, bosentan, BMS 182874, L-749329, SB209670) there was no correlation between the degree of discrepancy in K(B) and K(D) and structural class.

SIGNIFICANCE

For an antagonist to retain ET(A)-selectivity in vivo it may be necessary to identify those compounds that have at least 1000 fold ET(A):ET(B) selectivity in in vitro assays.

A novel cross-talk between endothelin and ErbB receptors controlling glutamate transporter expression in astrocytes

The endothelin and epidermal growth factor (EGF) systems are central to the control of reactive brain processes and are thought to partly exert these tasks by endothelin-induced transactivation of the epidermal growth factor receptor (EGFR) Here we show that beyond EGFR transactivation, endothelins prevent the ligand-induced internalization of the EGFR. We unravel that endothelins abrogate internalization of the EGFR by either promoting the formation of "internalization-deficient" EGFR/ErB2-heterodimers or by activating c-Abl kinase, a negative regulator of EGFR internalization. We further provide evidence that this cross-talk is operational in the control of astrocytic glutamate transport. Specifically, we establish that the inhibitory effects exerted by endothelins on basal as well as EGF-induced expression of the major astroglial glutamate transporter subtype, glutamate transporter 1, are a direct consequence of the endothelin-dependent retention of the EGFR at the cell surface. Together our findings unravel a previously unknown cross-talk between endothelin and epidermal growth factor receptors, which may have implications for a variety of pathological conditions.

Preproendothelin-1 expression is negatively regulated by IFNγ during hepatic stellate cell activation

Endothelin-1 (ET-1), a powerful vasoconstrictor peptide, is produced by activated hepatic stellate cells (HSC) and promotes cell proliferation, fibrogenesis, and contraction, the latter of which has been thought to be mechanistically linked to portal hypertension in cirrhosis. Interferon-γ (IFNγ), a Th1 cytokine produced by T cells, inhibits stellate cell proliferation, fibrogenesis, and muscle-specific gene expression. Whether IFNγ-induced inhibitory effects are linked to regulation of ET-1 expression in activated stellate cells remains unknown. Here we examined IFNγ's effects on preproET-1 mRNA expression and the signaling pathways underlying this process. We demonstrated that preproET-1 mRNA expression in HSCs was prominently increased during cell culture-induced activation; IFNγ significantly inhibited both preproET-1 mRNA expression and ET-1 peptide production. Similar results were found in an in vivo model of liver injury and intraperitoneal administration of IFNγ. PreproET-1 promoter analysis revealed that IFNγ-induced inhibition of preproET-1 mRNA expression was closely linked to the AP-1 and Smad3 signaling pathways. Furthermore, IFNγ reduced JNK phosphorylation, which tightly was associated with decreased phosphorylation of downstream factors c-Jun and Smad3 and decreased binding activity of c-Jun and Smad3 in the preprpET-1 promoter. Importantly, IFNγ reduced both c-Jun mRNA and protein levels. Given the important role of ET-1 in wound healing, our results suggest a novel negative signaling network by which IFNγ inhibits preproET-1 expression, highlighting one potential molecular mechanism for IFNγ-induced host immunomodulation of liver fibrogenesis.

Endothelin-1 cooperates with hypoxia to induce vascular-like structures through vascular endothelial growth factor-C, -D and -A in lymphatic endothelial cells

AIMS

Lymphangiogenesis refers to the formation of new lymphatic vessels and is thought to constitute conduits for the tumor cells to metastasize. We previously demonstrated that endothelin (ET)-1 through its binding with ETB receptor (ET(B)R) expressed on lymphatic endothelial cells (LEC), induced cell growth and invasiveness. Since vascular endothelial growth factor (VEGF)-A/-C/-D, and hypoxia play key role in lymphatic differentiation, in this study we investigated the involvement of these growth factors and hypoxia in ET-1-induced lymphangiogenesis.

MAIN METHODS

Real time PCR and ELISA were used to quantify VEGF-A/-C/-D. LEC morphological differentiation was analyzed by tube formation assay on Matrigel.

KEY FINDINGS

Hypoxia, as well as ET-1, induced an increase in VEGF-A/-C and -D expression that was reduced in the presence of a selective ET(B)R antagonist, BQ788, and enhanced when ET-1 was administered under hypoxic conditions. We analyzed the role of hypoxia on LEC morphological differentiation, and found that hypoxia increased the formation of vascular-like structures on Matrigel and that in combination with ET-1 this effect was markedly enhanced. The use of specific antibodies neutralizing VEGF-A, or recombinant VEGFR-3/(Flt-4)/Fc that block VEGF-C/-D, inhibited the effect of ET-1 as well that of hypoxia.

SIGNIFICANCE

These results demonstrated that ET-1 and hypoxia act, at list in part, through VEGF to induce lymphangiogenic events and that these two stimuli may cooperate to induce VEGF-A/-C/-D expression and lymphatic differentiation. These data further support the role of ET-1 as potent lymphangiogenic factor that relies on the interplay with hypoxic microenvironment and with VEGF family members.

Peripheral mechanisms of itch

Detection of environmental stimuli that provoke an aversive response has been shown to involve many receptors in the periphery. Probably the least-studied of these stimuli are those that induce the perception of itch (pruritus), an often-experienced unpleasant stimulus. This review covers the ligands and their receptors which are known to cause primary sensory neuron activation and initiate itch sensation. Also covered are several itch-inducing substances which may act indirectly by activating other cell types in the periphery which then signal to primary neurons. Finally, progress in identifying candidate neurotransmitters that sensory neurons use to propagate the itch signal is discussed.

Comparison of endothelin receptors in normal versus cirrhotic human liver and in the liver from endothelial cell-specific ETB knockout mice

AIMS

Endothelin (ET) antagonists show promise in animal models of cirrhosis and portal hypertension. The aim was to pharmacologically characterise the expression of endothelin receptors in human liver, hepatic artery and portal vein.

MAIN METHODS

Immunofluorescence staining, receptor autoradiography and competition binding assays were used to localise and quantify ET receptors on hepatic parenchyma, hepatic artery and portal vein in human cirrhotic or normal liver. Additional experiments were performed to determine the affinity and selectivity of ET antagonists for liver ET endothelin receptors. An endothelial cell ET(B) knockout murine model was used to examine the function of sinusoid endothelial ET(B) receptors.

KEY FINDINGS

ET(B) receptors predominated in normal human liver and displayed the highest ratio (ET(B):ET(A) 63:47) compared with other peripheral tissues. In two patients examined, liver ET(B) expression was up-regulated in cirrhosis (ET(B):ET(A) 83:17). Both sub-types localised to the media of normal portal vein but ET(B) receptors were downregulated fivefold in the media of cirrhotic portal vein. Sinusoid diameter was fourfold smaller in endothelial cell ET(B) knockout mice. The liver morphology of ET(B) knockout mice was markedly different to normal murine liver, with loss of the wide spread sinusoidal pattern. In the knockout mice, sinusoids were reduced in both number and absolute diameter, while large intrahepatic veins were congested with red blood cells.

SIGNIFICANCE

These data support a role for the ET system in cirrhosis of the liver and suggest that endothelial ET(B) blockade may cause sinusoidal constriction which may contribute to hepatotoxicity associated with some endothelin antagonists.

Cellular localization of receptors using antibodies visualized by light and dual labeling confocal microscopy

Immunocytochemistry can be used to visualize the binding of specific site-directed antisera to receptors in tissue sections and permits the precise identification of cell types expressing a particular receptor when viewed using a conventional light microscope or by confocal microscopy. Protocols are also described for the dual labeling of cells in the same section using primary antisera raised in two different species (one to the receptor of interest, the second to an immunogen such as a cell-specific marker or the endogenous ligand) with the corresponding secondary antisera conjugated to different fluorescent dyes.The technique has a range of applications. Subtypes of receptors can be identified and distinguished prior to the development of selective agonists or antagonists, which is particularly important for mapping orphan receptors, where the identity of the endogenous ligand in not yet known. The deletion of genes encoding receptors, particularly in mice, has emerged as a powerful tool in understanding the role of a specific receptor in physiological processes. Receptor immunocytochemistry can be used to analyze the resulting phenotype in whole body sections of mice without preselection of the tissue to be studied.

Radioligand binding assays and their analysis

Radioligand binding is widely used to characterize receptors and determine their anatomical distribution, particularly the superfamily of seven transmembrane-spanning G protein-coupled receptors for both established transmitters such as endothelin-1 and an increasing number of orphan receptors recently paired with their cognate ligands. Three types of assay are described. In saturation experiments, tissue sections, cultured cells, or homogenates are incubated with an increasing concentration of a radiolabeled ligand, which can be a labeled analog of a naturally occurring transmitter, hormone, or synthetic drug. Analysis using iterative nonlinear curve-fitting programs, such as KELL, measures the affinity of the labeled ligand for a receptor (equilibrium dissociation constant, K ( D )), receptor density (B (max)), and Hill slope (nH). The affinity and selectivity of an unlabeled ligand to compete for the binding of a fixed concentration of a radiolabeled ligand to a receptor are determined using a competition binding assay. Kinetic assays measure the rate of association to or dissociation from a receptor from which a kinetic K ( D ) may be derived. Quantitative autoradiography and image analysis is a sensitive technique to detect low levels of radiolabeled ligands and determine the anatomical distribution of receptors in sections that retain the morphology of the tissue. The measurement of bound radioligand within discrete regions of autoradiographical images using -computer-assisted image analysis is described.

Endothelium-dependent vasoconstriction in isolated vessel grafts: a novel mechanism of vasospasm?

BACKGROUND

YC-1 (3-(5'-hydroxymethyl-2'furyl)-1-benzyl-indazole) is an allosteric activator of soluble guanylyl cyclase (sGC) and a vasodilator. This study describes a paradoxical action of YC-1 in isolated vessels of patients with coronary artery disease (CAD) that appears to trigger an endothelium-dependent vasoconstrictor pathway present in vessels with endothelial dysfunction.

METHODS

Effects of YC-1 on the tensions of isolated vessels were investigated in an organ bath. Vasoconstrictors released from the vessels were quantified through enzyme-linked immunosorbent assay.

RESULTS

YC-1 elicited long-lasting constriction in saphenous veins and radial arteries from patients with CAD, but not in human umbilical veins. The half-maximal effective dose was 1.0 μmol/L. Constriction was attenuated by nifedipine (an L-type Ca(2+)-channel blocker), bosentan (an endothelin [ET](A)/ET(B) inhibitor), BQ-788 (N-[(cis-2,6-Dimethyl-1-piperidinyl)carbonyl]-4-methyl-L-leucyl-1-(methoxycarbonyl)-D-tryptophyl-D-norleucine; an ET(B) inhibitor), and by denuding, but not by ODQ (1H-(1,2,4)oxadiazolo[4,3-a]quinoxalin-1-one; an inhibitor of sGC), BQ-123 (cyclo(-D-Trp-D-Asp-Pro-D-Val-Leu); an ET(A) inhibitor), or phosphoramidon (an endothelin converting enzyme inhibitor). Indomethacin (an inhibitor of cyclooxygenase-1 and -2) and SQ29,548 ([1S-[1α,2α(Z),3α,4α]]-7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid; a thromboxane receptor antagonist) suppressed YC-1-induced constriction, whereas DFU (5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone; a cyclooxygenase-2 inhibitor) had no effect. Rings of saphenous vein released significantly more endothelin-1 in the presence than in the absence of YC-1.

CONCLUSIONS

YC-1-induced vasoconstriction demonstrates the existence of an endothelium-dependent vasoconstrictor pathway in the blood vessels of patients with CAD that to date has been described only in animal models of hypertension. Patients with CAD who have elevated plasma levels of endothelin-1 are thus prone to endothelium-dependent vasoconstriction, which may also play a role in vasospasm in vascular grafts.

Contractile effects of endothelins on isolated human ureter

The aim of our study was to investigate mechanism of action of endothelins 1, 2 and 3 on spontaneous activity, tone and intraluminal pressure of human ureter. Both longitudinal tension and intraluminal pressure were recorded from the isolated segments of proximal human ureter. Endothelins 1, 2 and 3 (5.35x10(-11) M - 5.05x10(-8) M) produced concentration-dependent tonic contraction and sustained increase in intraluminal pressure of isolated preparations of human ureter. Endothelins 1 and 3 produced also concentration-dependent inhibition of spontaneous, phasic contractions of the isolated preparations. Selective antagonist of ET(A) receptors BQ123 and selective antagonist of ET(B) receptors BQ788 produced significant inhibition of endothelin-1-induced tonic contraction (pA(2)=8.80 and 6.55, respectively) and increase in intraluminal pressure (pA(2)=8.68 and 7.02, respectively), while they did not affect endothelin-1-induced inhibition of spontaneous activity. Endothelin 1 produces increase in tone and intraluminal pressure of isolated human ureter acting on both ET(A) and ET(B) receptors, the first one being functionally more important. Only endothelins 1 and 3 inhibit spontaneous, phasic activity of human ureter, but this effect was not blocked by selective antagonists of ET(A) and ET(B) receptors.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Gene Expression of the Endothelin-1 in Vasospastic Flap Pedicle – an Experimental Study on a Porcine Model

The aim of this study was to evaluate the amount of Endothelin-1 (ET-1) gene expression in the vasospastic vessel of the flap pedicle to prove or disprove the role of ET-1 gene expression in pathogenesis of mechanically induced vasospasm. The vasospasm was induced by the tension on the pedicle of the pedicled caudal superficial epigastric flap on 8 pigs. Laser Doppler was used for peripheral blood flow measurement. Specimens from the vasospastic vessel (group of specimens B) and from the flap border with no vasospasm (control group A) were taken 2 h after the stimulus initiation. Detection of ET-1 mRNA by Quantitative Real-Time RT-PCR was performed. β-actin was selected as an acceptable reference gene. Relative gene expression data were given as the n-fold change in transcription of target genes normalized to the endogenous control. Relative gene expressions and time indicators of vasospasm were compared in both groups. No significant difference of the ET-1 gene expressions was found between groups A and B (p = 0.505). No correlation between the duration of vasospasm and ET-1 gene expression was found as well (p = 0.299). In conclusion, the expression of the ET-1 gene in the mechanically induced vasospastic vessel of the pedicled flap was not significantly increased. In this study, the causality of the vasospasm pathogenesis and gene expression of ET-1 was not proven.

O-GlcNAcylation: a novel pathway contributing to the effects of endothelin in the vasculature

Glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAc) or O-GlcNAcylation on serine and threonine residues of nuclear and cytoplasmic proteins is a posttranslational modification that alters the function of numerous proteins important in vascular function, including kinases, phosphatases, transcription factors, and cytoskeletal proteins. O-GlcNAcylation is an innovative way to think about vascular signaling events both in physiological conditions and in disease states. This posttranslational modification interferes with vascular processes, mainly vascular reactivity, in conditions where endothelin-1 (ET-1) levels are augmented (e.g. salt-sensitive hypertension, ischemia/reperfusion, and stroke). ET-1 plays a crucial role in the vascular function of most organ systems, both in physiological and pathophysiological conditions. Recognition of ET-1 by the ET(A) and ET(B) receptors activates intracellular signaling pathways and cascades that result in rapid and long-term alterations in vascular activity and function. Components of these ET-1-activated signaling pathways (e.g., mitogen-activated protein kinases, protein kinase C, RhoA/Rho kinase) are also targets for O-GlcNAcylation. Recent experimental evidence suggests that ET-1 directly activates O-GlcNAcylation, and this posttranslational modification mediates important vascular effects of the peptide. This review focuses on ET-1-activated signaling pathways that can be modified by O-GlcNAcylation. A brief description of the O-GlcNAcylation biology is presented, and its role on vascular function is addressed. ET-1-induced O-GlcNAcylation and its implications for vascular function are then discussed. Finally, the interplay between O-GlcNAcylation and O-phosphorylation is addressed.

Endothelins participate in the central and peripheral regulation of submandibular gland secretion in the rat

We previously reported that endothelins (ETs) are involved in the rat central and peripheral regulation of bile secretion. In this study we sought to establish whether ET-1 and ET-3 modulated submandibular gland secretion when locally or centrally applied. Animals were prepared with gland duct cannulation to collect saliva samples and jugular cannulation to administer sialogogues. ETs were given either into the submandibular gland or brain lateral ventricle. Intraglandularly administered ETs failed to elicit salivation per se. However, ET-1, but not ET-3, potentiated both cholinergic- and adrenergic-evoked salivation through ET(A) receptors. ET-1 decreased cAMP content but increased phosphoinositide hydrolysis, whereas ET-3 attenuated both intracellular pathways. The expression of ET(A) and ET(B) receptor mRNAs as well as that of ETs was revealed in the submandibular gland by RT-PCR. Immunohistochemical studies showed that ET(A) receptor staining was localized around the interlobular ducts and acini, compatible with the myoepithelial cells' location, whereas ET(B) receptor staining was restricted to small blood vessels. When applied to the brain, both ETs induced no salivation but enhanced cholinergic- and adrenergic-evoked salivary secretion through parasympathetic pathways. ET-1 response was mediated by brain ET(A) receptors, whereas that of ET-3 was presumably through nonconventional ET receptors. Present findings show that ETs are involved in the brain regulation of cholinergic- and adrenergic-stimulated submandibular gland secretion through the activation of distinct brain ET receptors and parasympathetic pathways. However, when ETs were administered into the gland, only ET-1 enhanced cholinergic and adrenergic salivation likely through myopithelial cell contraction by activating ET(A) receptors coupled to phospholipase C. The presence of ETs and ET receptors suggests the existence of an endothelinergic system in the submandibular gland.

Current and future therapeutic options for persistent pulmonary hypertension in the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a potentially life-threatening condition that is characterized by supra-systemic pulmonary vascular resistance causing right-to-left shunting through the ductus arteriosus and/or foramen ovale, leading to a vicious cycle of hypoxemia, acidosis and further pulmonary vasoconstriction. Advances in neonatology including surfactant instillation, high-frequency ventilation, extracorporeal membrane oxygenation and, most importantly, inhaled nitric oxide (INO), have revolutionized the management of PPHN. However, given that INO does not improve oxygenation in a significant proportion (30-40%) of cases, there is an urgent need to consider other therapeutic options for PPHN. The issue is more important for developing nations with a higher PPHN-related health burden and limited resources. This article discusses the evidence about INO in term and preterm neonates in brief, and focuses mainly on the potential alternative drugs in the management of PPHN.

Doxorubicin selectively suppresses mRNA expression and production of endothelin-1 in endothelial cells

Doxorubicin (DXR) is a widely used cytostatic agent, but its administration is limited by its cardiovascular side effects. The endothelium is one of the largest organs in the human body and due to its direct contact with blood; it is exposed to the toxic effects of DXR. The aim of this study was to investigate in endothelial cells the effects of DXR on the expression of genes involved in cardiovascular diseases. We used in vitro cultured human umbilical vein endothelial cells (HUVEC) as a model; gene expression was assessed by SuperArray and qPCR. Out of the 96 representative genes of cardiovascular importance, the expression of only the ET-1 gene changed significantly. ET-1 mRNA expression was 10.9% of the untreated control (p=0.0049). This result was confirmed by qPCR (2.41% of control, p=0.0022). DXR also suppressed ET-1 production at protein level (p=0.0116). Both the early decrease in endothelial ET-1 production in the presence of DXR and the high plasma level of DXR during chemotherapy may influence the toxic effects of the drug.

Role of peripheral endothelin receptors in an animal model of complex regional pain syndrome type 1 (CRPS-I)

Chronic post-ischemic pain (CPIP) is an animal model of CRPS-I developed using a 3-h ischemia-reperfusion injury of the rodent hind paw. The contribution of local endothelin to nociception has been evaluated in CPIP mice by measuring sustained nociceptive behaviors (SNBs) following intraplantar injection of endothelin-1 or -2 (ET-1, ET-2). The effects of local BQ-123 (ETA-R antagonist), BQ-788 (ETB-R antagonist), IRL-1620 (ETB-R agonist) and naloxone (opioid antagonist) were assessed on ET-induced SNBs and/or mechanical and cold allodynia in CPIP mice. ETA-R and ETB-R expression was assessed using immunohistochemistry and Western blot analysis. Compared to shams, CPIP mice exhibited hypersensitivity to local ET-1 and ET-2. BQ-123 reduced ET-1- and ET-2-induced SNBs in both sham and CPIP animals, but not mechanical or cold allodynia. BQ-788 enhanced ET-1- and ET-2-induced SNBs in both sham and CPIP mice, and cold allodynia in CPIP mice. IRL-1620 displayed a non-opioid anti-nociceptive effect on ET-1- and ET-2-induced SNBs and mechanical allodynia in CPIP mice. The distribution of ETA-R and ETB-R was similar in plantar skin of sham and CPIP mice, but both receptors were over-expressed in plantar muscles of CPIP mice. This study shows that ETA-R and ETB-R have differing roles in nociception for sham and CPIP mice. CPIP mice exhibit more local endothelin-induced SNBs, develop a novel local ETB-R agonist-induced (non-opioid) analgesia, and exhibit over-expression of both receptors in plantar muscles, but not skin. The effectiveness of local ETB-R agonists as anti-allodynic treatments in CPIP mice holds promise for novel therapies in CRPS-I patients.